A method for forming a coating film by applying a coating material in order to protect the surface of various materials such as metals, inorganic materials, plastics, woods, paper, etc. or in order to impart a special function such as water and oil repellency, has been used since a long time ago. As a method for curing a coating film, a curing method by heating and a curing method by irradiation with active energy rays have been known. The latter has merits in that as compared with the former, the time required for curing is short, the occupying area in the coating line may be small, and since no heating is required, the substrate is not restricted, and therefore, it is recently widely used for the coating of various substrates as described above, and its application is actively studied in the field of coating of displays, covering of optical fibers or special coating of e.g. electronic components, electric wires, etc.
Heretofore, photocurable fluorinated polymer compositions have been proposed which comprise a fluorinated polymer having polymerizable unsaturated groups, an acrylic acid ester and a photoreaction initiator (Patent Documents 1 to 4). Such photocurable fluorinated polymer compositions have such a problem that they are susceptible to an inhibition reaction by oxygen in air, since the photocuring reaction proceeds by a radical polymerization mechanism, or such a drawback that the shrinkage at the time of curing is substantial.
On the other hand, photocurable fluorinated polymer compositions comprising a fluorinated polymer having epoxy groups, an epoxy compound and a photoreaction initiator, have been proposed (Patent Documents 5 and 6).
These photocurable fluorinated polymer compositions have such a merit that they are not susceptible to an influence of oxygen in air, since the photocuring reaction proceeds by a photocation polymerization mechanism of epoxy groups, and a cured product excellent in chemical resistance or adhesion to the substrate can be obtained, and thus, in recent years, they have been used in many applications. However, the photocation polymerization of epoxy groups is poor in the polymerization reactivity or photosensitivity as compared with photoradical polymerization of unsaturated groups, and after the treatment by irradiation with light, heat treatment was further required as post curing. Further, the epoxy compound or the epoxy group-containing monomer as the main material for the epoxy group-containing fluorinated polymer gives an influence to the working environment and thus presents difficulties in handling.